Bacteria that cause infectious diseases often grow in biofilms where the bacterial cells and their extracellular polymers are attached to biological or non-biological surfaces. Bacteria growing in biofilms demonstrate a variety of phenotypic differences compared to the same strains growing planktonically, including increased resistances to antimicrobials and to phagocytosis. This proposal is designed to elucidate the molecular mechanisms that enable bacteria to grow in biofilms and cause chronic, debilitating infections. Much progress has been made on the mechanisms used by bacteria to adhere to surfaces. However, there is little information about the physiological changes in bacterial that occur following bacterial adhesion and during biofilm development. We developed novel in situ genetic and microscopic methods to characterize the changes in gene expression that mediate these phenotypic changes. Using these novel selections, we isolated nine clones with fusions to genes that demonstrated a five-fold to thirty-fold increase in gene expression, following attachment of the opportunistic pathogen Pseudomonas aeruginosa to a surface. The goals of this proposal are designed to: (i) characterize the pathogen Pseudomonas aeruginosa to a surface. The goals of this proposal are designed to: (i) characterize the products of these surface-growth induced genes (sgi), (ii) determine the survival advantage imparted by sgis during biofilm development, and (ii) identify other changes in gene expression including gene repression, that occur during biofilm development of P. aeruginosa. Information provided by this research will increase our understanding of the physiology of bacteria growing in biofilms. This information will provide important targets for anti-microbials , either through inhibition of sgis required for biofilm development, or through aberrant induction of genes normally repressed during biofilm growth.